Heteroaggregation and photoelectric conversion of porphyrins on a nanostructured TiO2 electrode

The cosensitization of a nanostructured titanium dioxide (TiO₂) electrode with tetrasulphonated porphyrins (MTsPP M=Zn H₂) is reported. Cosensitization greatly enhances the photocurrent response at the Q-band of H₂TsPP and markedly decreases the photocurrent response in the Soret band of ZnTsPP. The photoelectric behavior of the cosensitized TiO₂ electrode is attributed to the formation of heteroaggregates between H₂TsPP and ZnTsPP molecules on the positively charged TiO₂ electrode by charge-transfer interaction resulting in the decrease of the surface concentration of the H₂TsPP dimer and the presence of the low-lying charge-transfer state.